Method for determining the activity of metallic catalysts



Patented Dec. 27, 1949 METHOD FOR DETERMINING THE ACTIVITY F METALLIC CATALYSTS Francis J. McNamara, Rosemont, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application August 24, 1946, Serial No. 692,877

(Cl. i1- 42) s claims. 1

This invention relates broadly to a method of measuring catalytic activity of metal surfaces and more particularly to a method of obtaining indications relative to the real surface area of metallic 'objects so that a maximum catalytic surface area of metallic surfaces as obtained by etching or other surface roughening processes may be indicated.

In many industrial and .chemical operations it is necessary to employ a metallic catalyst whose effectiveness is generally in direct proportion to its surface area. It is known that a metallic surface of average smoothness presents an apparent surface area which may be conveniently measured in terms of square inches, centimeters or the like. It is also known, however, that such apparent surface area is not equivalent to the catalytic surface area which is determined by.

the molecular condition of the surface, the freedom from resistant lm and the added physical surface resulting from chemical or mechanical roughening. In order to achieve greater eiliciency and economy in the use of metallic catalysts it has been proposed, therefore, that the surface of such metallic catalysts be treated to increase the catalytic surface area without increasing the apparent surface area. One method of preparing the surface of a metallic catalyst is to etch the surface in an acid bath or by a controlled electrolytic process. -When preparing the surface of a metallic catalyst by such etching processes, it is diicult to determine when a maximum catalytic surface is obtained beyond which a further etching will have no beneficial effect.

It is therefore a principal object of this invention to provide a simple and effective electrolytic method of obtaining an indication proportional to the real surface area to determine the -maximum catalytic surface area of a metallic object as produced by etching or other surface roughening processes.

Further objects and advantages of this invention will be apparent by reference to the following specification and drawing in which:

Figure 1 is a top plan view of the electrolytic apparatus of this invention and showing schematically the electrical wiring, and 1 Figure 2 is a side'elevation sectioned on the line 2-2 of Figure 1.

Referring to the drawings, the electrolytic apparatus is shown to comprise a glass jar IIJ containing an l electrolyte II and having metallic mounting strips I2 and I3 fastened to the lp Il of the Jar. If desired the jar may be formed of plastic or other electric insulating substance that is impervious to the electrolyte. The mounting strips I2 and I3 also function as electric terminals for the electrolytic apparatus and are adapted to be connected to a source of electric current. As shown in Figure l, mounting strip I2 is connected by the wire I5 to the negative terminal of an electric power supply such as a battery (not shown). The mounting strip I3 is connected by wire I6 in series with a current measuring device I1 and a rheostat I8 to the positive terminal of the electric power supply. A voltage measuring device I9 is connected between the two mounting strips I2 and I3. In the specific example of the invention to be described, the current measuring device is a milliammeter and the voltage measuring device is a millivoltmeter but the choice of such devices is of course determined by the magnitude of the currents and voltages to be4 measured.

On the inside ends of the mounting strips I2 and I3 are fastened depending spring clips 20 and 2|, which, being of metal, will conduct the electrolytic current to be passed from the mounting strip I2 through the electrolyte I I and to the mounting strip I3 when the terminals are connected as shown to a direct current source of power. The spring clips 20 and 2| enable the quick and easy attachment of the metal plates or electrodes 22 and 23.

The electrolytic apparatus as described above is in the nature of a conductivity cell. If the electrolyte Il is comprised of a very weak acid such as for example N/32 hydrochloric acid and a source of direct current is'connected to the strips l2 and I3, an electric current will ilow. The amount of electric current for a given applied voltage will be determined by the conductivity of the electrolytic apparatus which in this specific example is determined by the amount and the strength of the electrolyte acid, by the physical spacing of the electrodes and by the size or area of the electrodes in contact with the electrolyte. Also variations in temperature will cause changes in current ow for a given applied voltage.

In adapting the above described electrolytic apparatus to the method of this invention it is necessary that all the above mentioned variables such as temperature', applied voltage, electrode spacing and electrolyte volume and strength be rigidly fixed to known reference values. If all of the above variables are fixed to reference values and the metal electrode 22 is selected as a standard reference electrode of xed size and known 3l n real surface area in contact with the electrolyte, then the amountgof current owing in the cell will be directly proportional to the surface area of electrode 23 in contact .with the electrolyte. Assuming that various metallic plates of identical apparent surface area but different catalytic surface area are successively connected as the metal electrode 23, it will be found that a different eletric current will be passed through the electrolyte for each different plate used and that the current will be directly proportional to the catalytic surface area of the various vmetallic plates tested. Thus the electrolytic apparatus used by the method of this invention as described will indicate the catalytic surface area of a metallic plate or other metal object used in catalytic processes.

As a specific example of the use of this invention, consider'the following. In the defluorination of petroleum products, so-called aluminum Raschlg rings are used as catalysts. The preparation of these aluminum rings preliminary to their use as a catalyst requires treatment with HCl to increase the catalytic activity. When etching such rings with 6% HC1 it is diicult to determine when a maximum effective catalytically active surface is obtained, as apparently the surface is formed, gradually tears away, exposing a new surface to be etched, formed, etc. By periodically connecting the aluminum ring as the elecreading of the current ilow through said cell as a reference; removing said catalyst sample to an etching bath, returning the sample after etching and cleaning to the electrolytic cell,` taking a second reading of the current flow through said electrode of an electrolytic cell, the other eleccally connecting the aluminum ring as the electrode 23 in the apparatus of this invention and checking for a maximum current reading, an indication of the maximum effective surface can be obtained. When using the invention for this purpose, itwas found that a suitable operating procedure would be to adjust the rheostat I8 to obtain an applied voltage of 0.98 volt which would give a current ow of about 24 ma. through an electrolyte of N/32 HC1 when maximum real surface area forl the aluminum ring was obtained. It should also be mentioned that the standard reference electrode 22, when the invention was used for this purpose, was formed of an aluminum strip of a known and fixed reference surface area bothreal and apparent.

It should be noted, however, that the selection of metals for the electrodes 22 and 23 is not critical so long as the variables previously mentioned are xed to known values and the apparatus is properly calibrated against a standard or reference surface. Also the choice of electrolyte isV not critical except that the electrolyte should preferably be weak so as not to attack or etch the reference electrode 22 or the subject electrode 23 during the operation of the method of this invention since such etching would change the real surface area of either the reference electrode .or the electrode to be measured causing obvious diiliculties.

I claim:

,1. The method of determining the maximum catalytic activity of etched metallic catalysts which includes the steps of connecting an untreated sample of said metallic catalyst as one electrode of an electrolytic cell, the other electrode of said cell being xed therein and constituting a reference electrode, applying a xed'andY known voltage to the electrodes of saidfcell, said electrodes having a i'lxed spacing with relation to each other, the electrolyte of said cell being of known volume and of a limited strength to preserve the catalyst intact and pass electric current therethrough. maintaining the temperature of-said cell substantially constant, and taking a trode of said cell being xed therein and constituting a reference electrode, applying a nxed and known direct current voltage to the electrodes of said cell. said electrodes having a nxed spacing with relation to each other, the electrolyte of said cell being of known volume and of a limited strength to preserve the catalyst intact and pass electric current therethrough, maintaining the temperature of said cell substantially constant, and taking .a reading of the direct-current flow through said cell as a reference; removing said catalyst sample to an etching bath, returning the sample after etching and cleaning to the electrolytic cell, taking a second reading of the direct current flow through said cell, repeating said etching and cleaning operation together with additional current ilow readings until the maximum diiference in current flow reading is obtained, the highest reading indicating the most active catalytic condition for the catalyst.

3. The method of determining the maximum catalytic activity of etched metallic catalysts which includes the steps of connecting an untreated sample of said metallic catalyst as one electrode of an electrolytic cell, the other electrode of ysaid cell being xed therein and constituting a reference electrode, applying a fixed and known voltage to the electrodes of said cell, said electrodes having a ilxed spacing with rela.- tion to each other,the electrolyte of said cell being comprised of a known volume of hydrochloric acid having a strength in the order of N/32 to preserve the catalyst intact and pass electric current therethrough, maintaining the temperature of said cell substantially constant, and taking a reading of the current flow through said cell as a reference; removing said catalyst sample to an etching bath, returning the sample after etching and cleaning to the electrolytic cell, taking a second reading of the current flow through said cell, repeating said etching'and cleaning operation together with additional current ow readings until the maximum difference o in current iiow reading is obtained, the highest reading indicating the dition for the catalyst.

4. The method of determining the maximum catalytic activity of etched metallic catalysts which includes the steps of connecting an untreated sample of said metallic catalyst as one electrode of an electrolytic cell, the other electrode of'said cell being fixed therein and constltuting a reference electrode, applying a xed and known direct current voltage to the electrodes of said cell, said electrodes having a xed most active catalytic conspacing with relation to each other, the electrolyte of said cell being comprised of a known volume of hydrochloric acid having a strength of the order of N/32 to preserve the catalyst intact and ases-.co1

' pass electric current therethrough. maintaining the temperature of said'cell substantially conetant',` and taking a reading of the direct current catalytic activity of trennen metallic catalysts ow through said cell as a reference; removing e said catalyst sample to an etching bath,"returning the sample after etching and cleaning to the electrolytic cell, taking a second reading of the direct current flow through said cell, repeating v said etching-and cleaning operation together with additional current f lo'w readings until the maximum diiference in current now reading is obtained, the highest reading indicating the most active catalytic condition for the catalyst.

5. The method of determining the maximum catalytic activity of treated metalliccatalysts which includes the steps of connecting an un-2 treated sample of said metallic catalyst as one electrode of an 'electrolytic cell, the other electrode of said cell being fixed therein and constitutin'g a reference electrode, applying a ilxed and known voltage to the electrodes of said cell, said electrodes having a xed'spacing'with relation to c each other, the electrolyte of'said cell being of known volume and of a limited strengthto prein current ow from the reference reading of the untreated catalyst is obtained, the highest reading indicating the most active catalytic condition of the catalyst.

6. The method of determining the maximum catalytic activity of treated metallic catalysts which includes the steps of connecting an untreated sample of said metallic catalyst as one electrode of an electrolytic cell, the other electrode of said cell being ilxed therein and constituting a reference electrode, applying a nxed and known direct current voltage to the electrodes of said cell, said electrodes having a iixed spacing with relationto each other, the electrolyte of said cell being of known volume and of a limited strength to preserve the catalyst intact and pass electric current therethrough, maintaining the temperature of said cell substantially constant: and taking a reading of the direct current now through said cell as a reference; removing said catalyst sample for treatment of the surface to increase the catalytic activity thereof and replacing in said cell for a second reading of the amount of current passing therethrough; repeating said treatment and current flow read- 'ings until the maximum difference in current flow from the reference reading of the untreated catalyst is obtained, the highest reading indicating the most active catalytic condition of the catalyst.

'1. The method of determining the maximum temperature of said which includes thel steps of connecting an untreatedsample of said metallic catalyst as one electrode oi an electrolytic cell, the other electrode of said cell being fixed thereinv and c onstituting a reference electrode, applying a fixed and known voltage to the electrodes of said cell. said electrodes having a xed spacing with relation to each other, the electrolyte of said cell being comprised of a known'volu'me of hydrochloric acid,having a strength in the order of preserve Vthe catalyst intact and pass N/32 to electric current therethrough, maintaining the cell substantially constant, and taking a reading ofthe' current flow through said cell as alreference; removing said catalyst sample for treatment oi' the surface tcincrease the catalytic activity thereof and replacing in said erence reading .is obtained; the highest reading indicating thel cell for a second reading ofthe amountvv of current'passing therethrough, repeating said treatments and currentow readings until the maximum diiference in current flow over the reiof the untreated catalyst sample most active catalytic condition of the catalyst.

8. The method` of determining the maximum catalytic activity of treated metallic catalysts which includes the steps of connecting an untreated sample of saidmetallic catalyst as one electrode of an electrolytic cell, the other electrode oi' said cell being ilxed therein and constituting a reference electrode, applying a ilxed and known direct current voltage to the electrodesof said cell, said electrodes having a fixed spacing with relation to each other, the electrolyte of said r cell being comprised of a known volume of hydrochloric acid having a strength of the order of N/32 to preserve the catalyst intact and pass electric current therethrough, maintaining the temperature of said cell substantially constant and taking a reading of the direct current dow through said cell as a reference, removing said catalyst sample for treatment of the surface to increase the catalytic activity thereof and replacing in said cell for a second reading of the amount of current passing therethrough, repeating said treatments and current flow readings until the maximum difference in current flow over the reference reading of the untreated catalyst sample is obtained; the highest reading indicating the most active catalytic condition of the catalyst.

FRANCIS J. McNAMARA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,089,030 Angell Mar. 3, 1914 1,845,231 Browning Feb. 16, 1932 1,910,021 Legg May 23, 1933 2,211,394 Vogel Aug. 13, 1940 2,260,840 Rowe Oct. 28, 1941 

